(1) Field of the Invention
The invention relates to the use of a conventional fluorescent solar collector as an external building unit.
(2) Technical Considerations and Prior Art
Solar accumulators (solar collectors) are well known. Conventional solar collectors, however, exhibit the disadvantage that their sensitive surface must be oriented in correspondence with the position of the sun. In some cases, expensive tracking devices are required to accomplish this orientation.
Fluorescent solar collector systems have an advantage over other collector systems in that the fluorescent panels need not be aligned exactly in accordance with the position of the sun. Even incident rays directed obliquely with respect to the panel are absorbed by the panel and can contribute toward fluorescent excitation.
Fluorescent solar collectors generally consist of either a single fluorescent disk carrying photocells along its rim, or of a combination of several such disks. These disks are configured to absorb completely a portion of the short-wave solar spectrum, convert the same into long-wave radiation and emit the long-wave radiation. The photocells arranged on the rim of the disk are sensitive to such long-wave radiation. Each fluorescent center in the disk emits toward all sides. The portion of the radiation impinging on the surface of the panels at a total angle of reflection, or under a larger angle, is completely reflected by the surface and passes, after several reflections, into the photocells.
Such a conventional fluorescent solar collector is shown in FIG. 1 of the drawings. The fluorescent panel 1 can consist of a synthetic resin or of glass is provided with a fluorescence agent in the form of activating ions. Suitable glasses are silicate, borosilicate, borate, or phosphate glasses containing, as the activating ions, for example Yb.sup.3+, Nd.sup.3+, or Cr.sup.3+. German Patent DOS No. 3,305,853, incorporated herein by reference, discloses suitable glasses for fluorescent panels. These activating ions absorb the sunlight impinging from above and transform the solar energy into fluorescent energy. Referring again to FIG. 1, an activating ion is indicated at point 3 which emits fluorescent radiation in all directions. Two rays 4 and 5 are representative of all radiation emitted by the ion. By total reflection on the panel surfaces, the largest portion of the fluorescent radiation is conducted to the panel rim where the photocells 2a, 2b are arranged. Preferably, silicon cells and CdS/Cu.sub.2 S cells are employed, exhibiting maximum sensitivity in a spectral range of 550-1,000 nm and 450-900 nm, respectively. In order to keep losses at a minimum, the activating ions are selected so that the fluorescent radiation is within these spectral ranges. The electrical energy generated by the photocells is tapped by the terminals 6a, 6b.